This invention relates to an apparatus for dispensing a predetermined trace amount of a sample onto the surface of one or more reaction carriers arrayed in two dimensions, allowing each component contained in the sample to react with a predetermined substance to provide a reaction product of which the coloration or formation of precipitates, etc. is capable of being detected by optical means, and optically scanning the reaction product by optical scanning means to provide a reading of the density or formation pattern for each sample, whereby a qualitative and/or quantitative determination is made with regard to the reaction product.